1. Field of the Invention
Embodiments of the present invention relate to a method, medium, and apparatus controlling a spindle motor, and more particularly, to a method, medium, and apparatus controlling a spindle motor to rotate at a constant speed by changing a current gain of a spindle motor driver, in a disk drive, according to the operating environment of the spindle motor.
2. Description of the Related Art
Conventionally, as in U.S. Patent Publication No. 6,744,587, a motor control circuit has been used to control the application of drive current to a motor using parallel paths, each of which included a digital-to-analog converter operating over different dynamic gains according to angular velocity. Similarly, Japanese Patent Laid-Open Publication No. 2003-173640 discusses the controlling of a voice coil motor using gains of a digital-to-analog converter in a track-seek mode and a track-following mode of a disk drive.
Typically, disk drives rotate a medium, e.g., a disk, at a target frequency (RPM) and at a constant speed using a spindle motor, and apply write or read signals to a magnetic head over the constantly rotating disk. To rotate the disk at a more accurate speed, the current gain of a motor drive circuit should be changed.
In general, a separate sensor is not used for a spindle motor, rather, a current measurement value obtained by resistance is used to determine the value of current fed back to the motor drive circuit. The maximum value of current supplied to the motor is set according to the amount of sensor resistance, and the resolution of the current is determined according to the resolution of a digital-to-analog converter embedded in the motor drive circuit. Here, there is an interrelationship between the maximum current value and the resolution. Accordingly, the sensor resistance can be properly set to satisfy both the maximum current value and the resolution.
When controlling the speed of the spindle motor, to reach a target speed more quickly, a higher maximum current value is required. Conversely to accurately control a motor speed, a higher resolution is required, which requires a lower current value. Accordingly, current gain changes must be made with these two desires taken into consideration.
That is, the resolution is increased by setting a resistance value satisfying the required maximum current and by reducing a high current gain after startup. If the current gain is reduced, the maximum current value is limited, but the same resolution of the digital-to-analog converter is applied within a limited variable current range, thereby increasing the resolution of current. The increased current resolution makes more accurate control possible.
Accordingly, to efficiently drive the motor, the motor is controlled using a high current gain with a low resolution, which allows for the use of the maximum current, at the startup. However, once the motor reaches the target speed, the motor is precisely controlled using a low current gain, with the higher resolution being obtained through the current gain change.
That is, the conventional method of controlling the current gain of the spindle motor driver in the disk drive includes setting the current gain to the highest level to supply the maximum current during the startup, monitoring the rotational speed of the spindle motor, and reducing the current gain to perform precise control of the spindle motor speed once the rotational speed reaches the target speed.
However, such a conventional control algorithm generally does not encounter problems at room temperature and constant voltage, but problems do occur in low temperature environments when the frictional force between a fluid dynamic bearing and a shaft of the motor increases. Additional problems of low voltage environments are that power relatively decreases and the maximum current may become saturated, as shown in FIG. 7-8 where changes of a digital-to-analog converted spindle drive control signal Spin DAC of the spindle motor driver are illustrated in a normal state and in an abnormal (low temperature and low voltage) state. Consequently, the motor may fail to reach the target frequency or fail to operate at the desired constant speed.